Controlling the signal frequencies in television systems



Aug. 15, 1939. Y I MAGUIRE' 6 CONTROLLING THE SIGNAL FREQUENCIES IN TELEVISION SYSTEMS Filed April 26, 1938 Patented Aug. 15, 193% s1: rs

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Irwin Leonard Maguire, Elwood, Victoria, Australia Application April 26, 1938, Serial No. 204,451 In Australia and Great Britain March 6, 1934 4 Claims.

This application is a continuation in part of application, Ser. No. 9,475.

In television it is known that at the, transmitter, elementary picture elements or picture: points of an image may be successively scanned one at a time and that the light from these points can be directed upon a photo-sensitive element suitably connected by a transmitting channel to modulate a source of light located at the receiver. It is known also that the light at the receiver which falls upon a viewing screen can bear" ranged to be focussed to a point corresponding at any instant in dimension and location to the picture point which is being scanned at the transmitter. It is known, also that the luminescence of a picture point at the receiver viewing screen is proportional to the luminescence of the picture point being scanned at the transmitter. It is a known also that the frequency of the video signal and the amount of definition of the facsimile is proportional to the magnitude of the ratio of the area of the picture being transmitted relative to the area of the picture point. From these facts it will be seen that the definition of the picture will be high if the ratio of the area of picture being transmitted to that of the area of picture point is large, whereas the frequency of the video signal will be low if this ratio is small. Also it is known that the magnitude of the video signal and of the intensity of the light utilised at the receiver which is controlled by the video signal may be arranged to be proportional to the area of the picture points recreated at the receiver or scanned at the transmitter.

Further it is known that. two identical signals may be arranged so that their effects add together or neutralise one another, thus two signals may be superimposed on one anotherand utilised to control the luminescence of a lamp and its lumi' nescency may be increased to a greater extent than was possible if only one signal was utilised or the light may be annulled if the effects of the signals are arranged to neutralise one another. In television it is desirable to have a high definition for the pictures and to have video signals of 7 low frequency.

According to the present inventionlow frequency video signals are obtained by arranging that the area of the picture pointsscanned at duced at the receiver; the area scanned at the transmitter at any particular moment comprising a number of picture points disposed in line in the direction of scanning. This result is attained by arranging that at the transmitter similar areas of picture points in line of identical images are scanned and two video signals are separately transmitted, one of these areas being slightly longer than the other to the extent of one picture point. a At the receiver the two video signals are mixed to almost neutralise one another and to leave a remaining signal effect equivalent to the one picture point difference between the areas scanned,- and this latter signal is utilised for the recreation of the said picture point at the receiver.

The accompanying diagrammatic drawing indicates a simple form of arangement in accordance with the present invention.

The complete image from'su'bject at S for transmission is directed as a single beam B by lens L to bi-prism BP and from the latter two beams B and B (each equivalent to B) are directed to v rotating mirror drum MD and from the latter still as B and B to scanning apertures AB and AB in a fixed plate P and thence each as portions of beams B and B separately to photoelectric cells PE and PE v The modulated current from PE and PE is applied to broadcasting channels BC and BC received at R and R thence to mixer at M in which the two modulated currents are adjusted at same signal strength to almost neutralize one another but leaving a signal effect equivalent to one picture point as above described. This signal eil'ect, equivalent to the difference in the effect between above two modulated currents received by R and R is amplified at A and utilized to modulate a source of light at ML. The modulated single light beam from ML is directed to mirror drum RMD and from the latter to viewing screen VS.

As two separate complete images are applied on the plate P having scanning apertures at AB and AB and former scanning aperture (AB) has a length equivalent to one full line as at D on the subject at S and the latter aperture (AB has a shorter length to the extent of one picture point in a full line as at D it will be readily understood that the difference in effects at PE and PE will be equivalent to one picture element and this difference in effect is that selected at M and applied at VS.

The. diagram has been simplified by indicating a definition of six lines of four elements each at S,

the line D being the particular line which the mirror surface at MD directs to the scanning apertures at AB and A3 At the particular moment represented by the diagram picture elements a, b, c in line D appear in aperture AB and elements a and b in aperture AB and from above description that when the difference between the signals from AB and AB is obtained at M this difference will be equivalent to the single picture element c appearing on the viewing screen.

The scanning apertures AB and AB are shown arranged in line to register on identically placed areas or lines on the two images and are shown with an approximate sine wave contour.

The scanning apertures have ordinates normal to the direction of scanning proportioned according to the ordinates of a sine curve and a maximum ordinate corresponding to the width of line into which the image is resolved, the length of the aperture in the direction of scanning being approximately proportional to degrees from '0 to 90.

It will be understood that the scanning apertures at AB and AB need not necessarily have the sine wave or approximate sine wave contour mentioned, the essential characteristic being that one aperture has a length greater than the other aperture to the extent of the area of one picture point.

It will also be understood by those skilled in the art that in lieu of the mirror drum MD and apertured plate P, scanning of the beams B and B may be eiiected by the use of scanning discs having scanning apertures with abovementioned characteristics arranged in a spiral path in the discs.

I claim:

1. In television, means for separately setting up two identical images of the subject to be televised, a separate scanning device for scanning each of said images, said scanning devices arranged to simultaneously scan equivalent areas on said images, one scanning device scanning a greater area than the other to the extent of the area of one picture point, photo-electric sensitive means for converting light beams derived from the scanning devices into separate identifiable signals, means for transmitting said identifiable signals, also means for mixing said signals when received for cancelling out equivalents and leaving a remaining signal electrically equivalent to the beforementioned additional picture point and means using said remaining signal to modulate a light beam incident on a viewing screen.

2. In television, means for setting up two identical images of the subject to be televised, rotating reflecting surfaces on which said images are incident, scanning devices on which the images reflected from said reflecting surfaces are separately incident, scanning apertures in said scanning devices arranged to simultaneously and separately scan identical areas on said images with the scanning apertures of one scanning device covering an area greater than that of the scanning aperture in the other scanning device to the extent of one additional picture point, photoelectric sensitive means for converting light beams derived from the scanning devices into separate identifiable signals, means for trans mitting said identifiable signals, also means for mixing said signals when received for cancelling out equivalents and leaving a remaining signal electrically equivalent to the beiorementioned additional picture point and means using said remaining signal to modulate a light beam incident on a viewing screen.

3. In television, means for setting up two identical images of the subject to be televised, rotating reflecting surfaces on which said images are incident, a plate on which the images reflected from said reflecting surfaces are separately incident, said plate having a scanning aperture registering with each of said images, one of said apertures having a greater length than the other aperture to the extent of the area of one picture point, photo-electric means for converting light beams derived from the scanning devices into separate identifiable signals, means for ransmitting said identifiable signals, also means for mixing said signals when received for cancelling out equivalents and leaving a remaining signal electrically equivalent to the beforernentioned additional picture point and means using said remaining signal to modulate a light beam incident on a viewing screen.

4. In television, means for setting up two identical images of the subject to be televised, rotating reflecting surfaces on which said images are incident, a plate on which the images reflected from said reflecting surfaces are separately incident, said plate having a scanning aperture registering with each of said images, one of said apertures having a greater length than the other aperture to the extent of the area of one picture point, photo-electric means for converting light beams derived from the scanning devices into separate identifiable signals, means for transmitting said identifiable signals, also means for mixing said signals when received for cancelling out equivalents and leaving a remaining signal electrically equivalent to the beforementioned additional picture point, means for amplifying said remaining signal, a beam of light modulated by said amplified signal, rotating refleeting surfaces on which said modulated light is incident, said rotating reflecting surfaces deflecting said modulated light to a viewing screen.

IRWIN LEONARD MAGUIRE. 

